Direct positive photographic materials



United States Patent 3,506,451 DIRECT POSITIVE PHOTOGRAPHIC MATERIALSNobuo Sonia, Junichi Nakazawa, Yoshio Sato, and Yoshimi Kuwabara, Tokyo,and Hidehiko Ishikawa, Odawara-shi, Japan, assignors to Sankyo Co.,Ltd., and Konishirokn Photo Industry Co., Ltd., both of Tokyo, Japan,both corporations of Japan No Drawing. Filed Mar. 13, 1967, Ser. No.622,437 Claims priority, application Japan, Mar. 19, 1966, 41/ 17,041Int. Cl. G03c 1/36 U.S. Cl. 96-101 11 Claims ABSTRACT OF THE DISCLOSUREA direct positive photographic element comprising a fog silver halideemulsion containing as a deep sensitizer 1,3 substituted-2,3-dihydro-2oxocycloheptimidazolium salts.

This invention relates to a direct positive light-sensitive silverhalide photographic material which comprises a support and, coatedthereon, a light-sensitive silver halide emulsion layer containingfogged silver halide crystals, said layer having a desensitizerincorporated therein, said desensitizer being a compound represented bythe general formula wherein R is alkyl, substituted or unsubstitutedaryl, or substituted or unsubstituted aralkyl radical; R is substitutedor unsubstituted aryl radical or substituted or unsubstituted aralkylradical; R is hydrogen, halogen, alkyl or phenyl radical; and X is ananion. It is the principal object of the invention to provide a directpositive, light-sensitive silver halide photographic material havinghigh reversal sensitivity and high contrast and being free from anystaining of photographic surface.

A direct positive, light-sensitive silver halide photographic materialof the kind specified, which comprises a fogged silver halide emulsion,can directly yield a positive image through a single exposure and singledevelopment by utilization of Herschel effect, solarization, dyereversal (spectrally sensitized reversal), etc. In order to acceleratethese actions, it is well known to incorporate an appropriatedesensitizer into the fogged silver halide emulsion before coating.

Heretofore, a number of compounds have been known useful asdesensitizers for direct positive light-sensitive silver halidephotographic materals, which compounds include, for example,phenosafranine, malachite green, pinacryptol yellow, pinacryptol green,etc. These known desensitizers suffer from several drawbacks and are notsatisfactory in their actual use. For instance, phenosafranine which isa substance having red color usually causes reddish coloration of thephotographic materials, sometimes wtih decrease in contrast. Marachitegreen and pinacryptol green, both of which are green compounds, willdecrease whiteness of the background of photographic pictures.Furthermore, pinacryptol green sometimes has an adverse effect againststability of a fogged emulsion. Pinacryptol yellow, which is a generallypreferred known desensitizer because of its raising no problem incontrast of photographic images, will cause yellowish coloration todecrease whiteness of the surface ice of photographic materials. Thus,all the known desensitizers are not satisfactory because of theirundesired influence on the photographic properties.

We have now found that a compound of the general formula I'm wherein R RR and X- are defined as above can be used as a densitizer for a directpositive, light-sensitive silver halide photographic material, withoutcausing any contamination or coloration of photographic images and anyadverse influence on the photographic properties.

Thus, in accordance with the present invention, there is provided adirect positive, light-sensitive silver halide photographic materialwhich comprises a light-sensitive silver halide emulsion layercontaining fogged silver halide crystals and having a compound of theabove general formula, as a desensitizer, incorporated therein.

The compounds defined above are available at relatively low costs.Almost all of these are colorless substances, but a few have a verysight color insufiicient to cause coloration. The compounds can meet thefollowing requirements:

(1) They have a capability to decrease photographic sensitivity;

(2) They do not cause fogging or decrease in contrast;

(3) They do not cause any adverse effect on fogged silver halidecrystals;

(4) They can accelerate Herschel effect, solarization and dye reversal,and markedly improve the sensitivity of a direct positivelight-sensitive photographic material; and

(5) They are water-soluble.

A compound of the above general formula can be prepared according to themethod described in Chemical & Pharmaceutical Bulletin vol. 13, No. 7,pages 819-820, that is by the reaction of a troponeimine derivative ofthe formula NHRI M.P. 182 C.

1metl1y1-3-henzyl2,3-dihydro-2-oxocycloheptimidaz oliummonomethylsulfate (12) OCH;

ACHB

MI. 275 C.

1,3 di p-a-nisyl) -2,3 dihydro-2'oxocycloheptimidazollum chloride:

CH; 111 KOIBI- 1-methy1-3-benzyl-2,3-dihydro-2-oxocyc1oheptimidazoliumbromide M.P. 233 C. 1 methyl-3-beuzyl2,3-dihydfio2-oxocycloheptimidazolium 10 1 r N W /-O-C1- N BK M.P. 232C. (decomp.)

1,3-dibenzyl-6hromo-2,3-dihydro-2-0Xocycl0heptimidazolium chloridesensitizer will be within the range of 0.005 to 0.5 g. per 100 g. ofsilver nitrate, the amount of which is calculated from the silver halidecontained in the emulsion. However, this is not so a strict range and itis possible, with out any adverse effect, to use an amount slightlyoutside of said range. Usually it is preferred to dissolve thedesensitizer in water, or a water-miscible organic solvent (e.g. a loweralcohol or acetone) or the mixture of both to have a solution which isthen added to the emulsion containing fogged silver halide crystals.Other suitable additives or adjuvants, e.g. stabilizer, coating aid,film hardener, matting agent, etc., can be used in combination with thedesensitizer. The thus prepared emulsion is coated on a suitable supportin the manner known per se and then dried, thereby to obtain a directpositive, lightsensitive silver halide photographic material, which isentirelyfree from any staining or coloration of photographic surfacesand which can yield a Very clear positive image with high contrast andwith high whiteness of the reversed portion.

The following examples describe certain ways in which the principle ofthe invention has been applied, but are not to be construed as limitingits scope.

EXAMPLE 1 One kilogram of a pure silver chloride emulsion containing theequivalent to 40 g. of silver nitrate was buffered to pH 8.0 by theaddition of 30 m1. of 6% aqueous sodium metaborate solution. Thisemulsion was added further with 7 ml. of 3% formalin and heated at 50 C.for 60 minutes. The thus fogged emulsion was buffered to pH 6.0 with 10%aqueous citric acid solution and then divided to ten portions, each ofwhich was added with the compound indicated in Table 1. The respectiveportions were coated on photographic papers and then dried. The thusprepared ten direct positive, light-sensitive photographic sheets weresubjected to stepwise exposure to light through a filter (Toshiba UY-47)which can pass a light having a wave length of longer than 450 my andthen treated by development under fully same condition. Thesensitometric results obtained are set forth below:

As apparent from the above, the sheets according to the presentinvention were more excellent in the reversal sensitivity and contrastthan the control sheets. In addition, the sheets of the invention wereentirely safe from coloration, whereas the control sheet loaded withpinacryptol yellow or safranine suffered from yellowish or reddishcoloration.

EXAMPLE 2 One kilogram of a silver chloroiodide emulsion containing theequivalent to 40 g. of silver nitrate was buffered to pH 7.5 by theaddition of 25 cc. of 5% aqueous sodium carbonate solution. 10 ml. of 3%formalin was also added thereto and the resulted emulsion was heated at55 C. for 40 minutes. The fogged emulsion was divided to ten portions,each of which was added with the compound indicated in Table 2. Therespective portions were coated on photographic papers and then dried.The thus prepared ten direct positive, light-sensitive photographicsheets were subjected to imagewise exposure to White light and thentreated with a developing solution. The sensitometric results obtainedare set forth below:

As apparent from the above table, the sheets according to the presentinvention were more excellent in the reversal sensitivity and contrastthan the control sheets and further they were entirely safe from anycoloration.

What we claim is:

1. A direct positive, light-sensitive silver halide photographicmaterial which comprises a support and, coated thereon, alight-sensitive silver halide photographic emulsion layer containingfogged silver halide crystals and a desensitizing amount of a compoundof the general formula wherein R is alkyl, substituted or unsubstitutedaryl or substituted or unsubstituted aralkyl; R is substituted orunsubstituted aryl or substituted or unsubstituted aralkyl; R ishydrogen, halogen, alkyl or phenyl; and X- is an anion.

2. A direct positive, light-sensitive silver halide photographicmaterial as claimed in claim 1, wherein R and R are benzyl, R ishydrogen and X- is chloride.

3. A direct positive, light-sensitive silver halide photographicmaterial as claimed in claim 1, wherein R is p- 8 chlorobenzyl, R isp-methoxybenzyl, R is hydrogen and X- is chloride.

4. A direct positive, light-sensitive silver halide photographicmaterial as claimed in claim 1, wherein R is benzyl, R isp-methoxybenzyl, R is hydrogen and X- is chloride.

5. A direct positive, light-sensitive silver halide photographicmaterial as claimed in claim 1, wherein R is benzyl, R is p-tolyl, R ishydrogen and X- is chloride.

6. A direct positive, light-sensitive silver halide photographicmaterial as claimed in claim 1, wherein R is benzyl, R isp-chlorobenzyl, R is hydrogen and X- is chloride.

7. A direct positive, light-sensitive silver halide photographicmaterial as claimed in claim 1, wherein both of R and R arep-chlorophenyl, R is hydrogen and X is chloride.

8. A direct positive, light-sensitive silver halide photographicmaterial as claimed in claim 1, wherein R is benzyl, R is p-nitrobenzyl,R is hydrogen and X is chloride.

9. A direct positive, light-sensitive silver halide photographicmaterial as claimed in claim 1, wherein R is phenyl, R isp-chlorobenzyl, R is hydrogen and X is chloride.

10. A direct positive, light-sensitive silver halide photographicmaterial as claimed in claim 1, wherein R is p-chlorobenzyl, R isp-methylbenzyl, R is hydrogen and X- is chloride.

11. A direct positive, light-sensitive silver halide photographicmaterial as claimed in claim 1, wherein both of R and R are p-tolyl, Ris hydrogen and X is halide.

References Cited UNITED STATES PATENTS 3,284,203 11/1966 Takao et al96-101 X 3,367,779 2/1968 Nakazawa et al 96101 X NORMAN G. TORCHIN,Primary Examiner R. E. FIGHTER, Assistant Examiner U.S. Cl. X.R.

